Image forming apparatus and sheet feeding method

ABSTRACT

The present invention has been made to provide an image forming apparatus and a sheet feeding method capable of feeding a sheet without any problem even in the case where the rear end of the sheet is held between separating rollers at the time when the sheet is fed for a transfer process after aligning control.  
     An image forming apparatus comprises a drive controller  101  that controls the drive of feeding rollers disposed on the upstream side in the feeding direction relative to an intermediate feeding roller that feeds a sheet to a regist roller that performs skew correction for the sheet; and a timing determination section  102  that determines the timing at which the regist roller starts feeding the skew corrected sheet after the skew correction. When the timing determination section  102  determines that a predetermined timing for the regist roller to start feeding the skew corrected sheet has come, the drive controller  101  drives the feeding rollers by a predetermined time from the predetermined timing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus and, more particularly, to an image forming apparatus such as a digital copying machine or printer.

2. Description of the Related Art

In a conventional image forming apparatus, the following printing controls are used: a one-side printing control that performs printing for only the front side of a printing sheet (without performing for the back side thereof) and discharges the sheet outside the apparatus; another one-side printing control that performs printing for only the front side of a sheet (without performing for the back side thereof) and discharges the sheet according to the page number with the front and back sides of the printing sheet reversed; and a duplex printing control that does not discharge a printing sheet onto which printing has been performed but allows the printing sheet to pass through an ADU (Automatic Duplexing Unit) and resupplies the printing sheet for a printing process onto the back side thereof and discharges it outside the apparatus after the printing process.

In order to satisfy various conditions involving the above controls, the following three sheet feeding speed modes are specified in accordance with the requirements of the respective controls.

(1) Sheet supply speed: speed at which a printing sheet is fed from a sheet supply cassette to a regist roller at the time of sheet supply

(2) Process speed: speed at which a printing process (printing by transfer) is performed onto a printing sheet using a photoconductor drum and the like

(3) ADU speed: re-supply speed from the ADU

If a plurality of clutches are used to drive all the feeding rollers that feed a printing sheet together with multistage speed control, or a pulse motor is used to free change the speed of the feeding rollers in the conventional image forming apparatus, it is not impossible to adequately set the abovementioned three speeds so as to satisfy the conditions of the respective printing processes. However, these configurations may increase cost. As a countermeasure, as shown in FIG. 6, an intermediate feeding roller 112 (basically, a single intermediate feeding roller is used, but a plurality of intermediate feeding rollers may be used), which is driven by a pulse motor and disposed between a sheet discharge port at which the sheet discharges of a sheet feeding path 150 of the image forming apparatus and an ADU 170 meet and a regist roller 111, is used to perform sheet feeding operation at the above three sheet feeding speeds (three-speed control).

In the conventional image forming apparatus shown in FIG. 6, printing sheets housed in sheet supply cassette 161, 162, or the like are picked up by pick-up roller 141 c, 142 c, or the like and fed, one by one, to the sheet feeding path 150 by sheet supply rollers 141 a, 142 a, or the like and separating rollers 141 b, 142 b, or the like. The printing sheet that has been fed to the sheet feeding path 150 is fed by a first, second, feeding rollers 151, 152, at sheet supply speed (in this example, 420 mm/sec), fed by the intermediate feeding roller 112 at 420 mm/sec, and reaches the regist roller 111.

When having reached the regist roller 111, the printing sheet is subjected to aligning control and, after that, fed to a transfer nip between a photoconductor drum 110 and a transfer belt 120 by the regist roller 111 and intermediate feeding roller 112 at process speed (340 mm/sec), where a toner image is transferred onto the surface of the printing sheet. After that, the printing sheet is fed to a fixing unit followed by toner image fixing thereto. In the case of duplex printing, the printing sheet front side of which a toner image has been printed and fixed is reversed by the ADU 170 and resupplied, through the intermediate feeding roller 112, to the regist roller 111 at ADU resupply speed (385 mm/sec). After toner image printing and fixing processes are performed onto the back side of the printing sheet, the sheet is discharged outside the apparatus. This three-speed control is shown in the velocity diagram of FIG. 7.

However, in the case where a large-sized printing sheet (A3, LD) is fed from the sheet supply cassette to the transfer nip in the conventional image forming apparatus, a situation in which the rear end of the printing sheet has not been passed through the sheet supply/separating rollers at the time point when the aligning control for the printing sheet has been completed occurs (in FIG. 6, the printing sheet is held by the sheet supply roller 142 a/separarting roller 142 b by a length DS). In such a case, even if a clutch 151 c and 152 c (refer to FIG. 7) for the first and second feeding rollers 151 and 152 are in “OFF” state, a load (torque load: 0.45 to 0.5 mNm) applied when the sheet is being held between the sheet supply roller 142 a/separating roller 142 b is large enough to be likely to cause step-out of the pulse motor that drives the intermediate feeding roller.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above problem, and an object thereof is to provide an economical image forming apparatus and sheet feeding method capable of reducing a load applied on the rear end portion of a printing sheet when it is being held by sheet supply/separating rollers in the case where feeding operation of a printing sheet by the intermediate feeding roller and regist roller is restarted in a state where the rear end of a large-sized printing sheet has not been passed through between the sheet supply/separating rollers and still held by the rollers even at the time point when the aligning control for the printing sheet has been completed and thereby capable of realizing satisfactory printing sheet feeding operation.

To solve the above problem, according to a first aspect of the present invention, there is provided an image forming apparatus comprising: a drive controller that controls the drive of feeding rollers disposed on the upstream side in the feeding direction relative to an intermediate feeding roller that feeds a sheet to a regist roller that performs skew correction for the sheet; and a timing determination section that determines the timing at which the regist roller starts feeding the skew corrected sheet after the skew correction, wherein when the timing determination section determines that a predetermined timing for the regist roller to start feeding the skew corrected sheet has come, the drive controller drives the feeding rollers by a predetermined time from the predetermined timing.

According to a second aspect of the present invention, there is provided an image forming apparatus comprising: a drive controller that controls the drive of feeding rollers disposed on the upstream side in the feeding direction relative to an intermediate feeding roller that feeds a sheet to a regist roller that performs skew correction for the sheet; a sheet size determination section that determines the sheet size in the feeding direction of a sheet to be subjected to the skew correction performed by the regist roller; and a timing determination section that determines the timing at which the regist roller starts feeding the skew corrected sheet after the skew correction, wherein in the case where the sheet size determination section determines that a sheet to be subjected to the skew correction performed by the regist roller is larger than a predetermined size, when the timing determination section determines that a predetermined timing for the regist roller to start feeding the skew corrected sheet has come, the drive controller drives the feeding rollers by a predetermined time from the predetermined timing.

According to a third aspect of the present invention, there is provided a sheet feeding method comprising: a drive control step that controls the drive of feeding rollers disposed on the upstream side in the feeding direction relative to an intermediate feeding roller that feeds a sheet to a regist roller that performs skew correction for the sheet; and a timing determination step that determines the timing at which the regist roller starts feeding the skew corrected sheet after the skew correction, wherein when the timing determination step determines that a predetermined timing for the regist roller to start feeding the skew corrected sheet has come, the drive control step drives the feeding rollers by a predetermined time from the predetermined timing.

According to a fourth aspect of the present invention, there is provided a sheet feeding method comprising: a drive control step that controls the drive of feeding rollers disposed on the upstream side in the feeding direction relative to an intermediate feeding roller that feeds a sheet to a regist roller that performs skew correction for the sheet; a sheet size determination step that determines the sheet size in the feeding direction of a sheet to be subjected to the skew correction performed by the regist roller; and a timing determination step that determines the timing at which the regist roller starts feeding the skew corrected sheet after the skew correction, wherein in the case where the sheet size determination step determines that a sheet to be subjected to the skew correction performed by the regist roller is larger than a predetermined size, when the timing determination step determines that a predetermined timing for the regist roller to start feeding the skew corrected sheet has come, the drive control step drives the feeding rollers by a predetermined time from the predetermined timing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing an embodiment of an image forming apparatus according to the present invention;

FIG. 2 is a block diagram showing the functional configuration of the image forming apparatus according to the embodiment;

FIG. 3 is a flowchart for explaining a process flow in a sheet feeding method according the embodiment;

FIG. 4 is a cross-sectional view showing a state where aligning control for a large-sized printing sheet is performed in the image forming apparatus of FIG. 1;

FIG. 5 is a timing chart for explaining the operation of the image forming apparatus of FIG. 1;

FIG. 6 is a cross-sectional view for explaining a problem occurring in a conventional image forming apparatus; and

FIG. 7 is a timing chart showing the operation of the image forming apparatus of FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view showing the entire configuration of an image forming apparatus according to the embodiment of the present invention.

An image forming apparatus 100 of FIG. 1 has a toner image forming section including a photoconductor drum 10, a transfer belt 20 that transfers a toner image formed on the photoconductor drum 10 onto a printing sheet, a fixing unit 30 that fixes the toner image on the printing sheet onto which the toner image has been transferred and which has been fed by the transfer belt 20, a controller (constituted by a CPU and the like) 104 that performs various processing in the image forming apparatus 100, and a MEMORY 105, which is constituted by a ROM or RAM, stores various data and programs utilized in the image forming apparatus.

The image forming apparatus 100 further has a plurality of sheet supply cassettes that house printing sheets of various sizes, a sheet supply mechanism that draws printing sheets from one of the sheet supply cassettes and sequentially feeds them one by one to a sheet feeding path 50, a sheet feeding mechanism that feeds the printing sheets that has been supplied from the sheet supply mechanism to an aligning position through the sheet feeding path 50 at sheet supply speed (in this example, 420 mm/sec) and feeds the sheet after aligning control to a transfer nip between the photoconductor drum 10 and transfer belt 20 at process speed (in this example, 340 mm/sec), and an automatic duplexing unit 70 (for example, a stackless-type ADU 70) that reverses the printing sheet onto one side of which a toner image has been printed and resupplies the sheet to the aligning position in cooperation with an intermediate feeding roller 12 at ADU speed (resupply speed; in this example, 385 mm/sec).

The above sheet supply mechanism is constituted by sheet supply cassettes 61, 62, 63, 64, pick-up rollers 41 c, 42 c, 43 c, 44 c, sheet supply rollers 41 a, 42 a, 43 a, 44 a, and separating rollers 41 b, 42 b, 43 b, 44 b. The sheet feeding mechanism is constituted by a first, second, third, fourth feeding rollers 51, 52, 53, 54, the intermediate feeding roller 12, and a regist roller 11. In this case, the intermediate feeding roller 12 is driven by a pulse motor, and the CPU (controller) 104 can drive the intermediate feeding roller 12 at at least three speeds.

An inexpensive commonly-used motor (servo motor, etc.) is used to drive the first, second, third, fourth feeding rollers 51, 52, 53, 54 through a clutch mechanism, thereby reducing cost. In the duplex printing control, the automatic duplexing unit 70 resupplies the regist roller 11 with a printing sheet, the front and back sides of which has been reversed and which has been fed thereto through a route 32, 33, and 71, in cooperation with the intermediate feeding roller 12 at ADU speed. Therefore, the intermediate feeding roller 12 is configured to operate at three speeds of sheet supply speed, process speed, and ADU speed to meet the respective processing.

FIG. 2 is a block diagram showing the functional configuration of the image forming apparatus according to the embodiment. The image forming apparatus according to the embodiment includes a drive controller 101, a timing determination section 102, and a sheet size determination section 103.

The drive controller 101 has a role of controlling feeding rollers disposed on the upstream side in the feeding direction relative to the intermediate feeding roller 12 that feeds a sheet to the regist roller 11 that performs skew correction for the sheet. The feeding rollers disposed on the upstream side in the feeding direction relative to the intermediate feeding roller 12 include, for example, feeding rollers 51 to 54, sheet supply rollers 41 a to 44 a, separating rollers 41 b to 44 b, and pick-up rollers 41 c to 44 c. The drive controller 101 controls the drive of at least one type of these rollers.

The timing determination section 102 has a role of determining the timing at which the regist roller 11 starts feeding a sheet after skew correction.

The sheet size determination section 103 has a role of determining the sheet size in the feeding direction of a sheet to be subjected to the skew correction performed by the regist roller 11. The information relating the sheet size in the feeding direction thereof can be acquired from the sheet supply cassette from which the sheet is supplied, or sheet setting information defined by information of the image to be formed on the sheet.

In the case where the sheet size determination section determines that a sheet to be subjected to the skew correction performed by the regist roller 11 is larger than a predetermined size, when the timing determination section determines that a predetermined timing for the regist roller 11 to start feeding the skew corrected sheet has come, the drive controller 101 drives feeding rollers by a predetermined time from the predetermined timing. The feeding rollers in this case include, as above, feeding rollers 51 to 54, sheet supply rollers 41 a to 44 a, separating rollers 41 b to 44 b, and pick-up rollers 41 c to 44 c, and the drive controller 101 drives at least one type of these rollers.

Next, the entire processing flow in the sheet feeding method according to the present embodiment will be described. FIG. 3 is a flowchart for explaining a process flow in a sheet feeding method according the embodiment.

The drive controller 101 controls the drive of the feeding rollers disposed on the upstream side in the sheet feeding direction relative to the intermediate feeding roller 12 that feeds a sheet to the regist roller 11 that performs skew correction for the sheet (drive control step) (S801).

The sheet size determination section 103 determines the sheet size in the feeding direction of a sheet to be subjected to the skew correction performed by the regist roller 11 (sheet size determination step) (S802).

The timing determination section 102 determines the timing at which the regist roller 11 starts feeding a sheet after skew correction (timing determination step) (S803). In this case, data relating to the timing chart that defines the above sheet feeding timing is stored in the MEMORY 105.

When the sheet size determination step determines that a sheet to be subjected to the skew correction performed by the regist roller 11 is larger than a predetermined size, the drive controller 101 drives feeding rollers by a predetermined time from a predetermined timing at the time period when the timing determination step determines that the predetermined timing for the regist roller 11 to start feeding the skew corrected sheet has come (drive control step) (S804).

Here, a sheet larger than a predetermined size is, for example, an A3 size sheet. Further, a predetermined time is a time needed from a predetermined timing to the time for the rear end of a sheet to be released from between the separating rollers in the case where the rear end of the skew corrected sheet is, at the predetermined timing, held between the separating rollers that supply the sheet to the sheet feeding path.

The timing determination step (S803) is performed after the sheet size determination step (S802) in the above configuration. Alternatively, however, the sheet size determination step may be performed after the timing determination step, or the two steps may be performed at the same time.

The processing of the respective steps (S801 to S804) in the above sheet feeding method is realized when the CPU 104 executes a sheet feeding program stored in the MEMORY 105.

FIG. 4 is a cross-sectional view showing a state where aligning control for a large-sized printing sheet is performed in the image forming apparatus of FIG. 1, and FIG. 5 is a timing chart for explaining the operation of the image forming apparatus of FIG. 1.

How the controller in the image forming apparatus 100 having the above configuration copes with the problem as shown in FIG. 6 will be described with reference to FIGS. 1, 4, and 5. At time t1 shown in FIG. 5, a sheet supply motor that drives the feeding rollers 51 to 54 starts operating and clutches 51 c and 52 c (refer to FIG. 5) for the first and second feeding rollers 51 and 52 are turned “ON” to allow the first and second feeding rollers 51 and 52 to perform sheet feeding operation at sheet supply speed. At time t6, an intermediate feeding SW is also turned “ON”, and the first and second feeding rollers 51 and 52 feed a large-sized printing sheet to an aligning position (pre-regist SW “ON”; time t8) in cooperation with the intermediate feeding roller 12 during time t6 to time t9. The intermediate feeding SW is a sensor for determining whether the leading end of a sheet has been passed through the intermediate feeding roller 12, and the pre-regist SW is a sensor for detecting that a sheet has reached the position immediately before the regist roller 11.

During time t8 to t9, aligning control is performed. After the aligning control has been completed, the clutches 51 c and 52 c are turned “OFF” at time t9. At time t10, the regist roller 11 and intermediate feeding roller 12 intend to feed the printing sheet that has been subjected to the aligning control to the transfer nip between the photoconductor drum 10 and transfer belt 20 at process speed. During the time period when the sheet feeding to the transfer nip is started, that is, during time t10 to t11, the clutches 51 c and 52 c for the first and second feeding rollers 51 and 52 are turned “ON” to apply a force in such a direction to draw out the rear end of the printing sheet, which is held between the sheet supply roller 42 a and separating roller 42 b as shown in FIG. 4, thereby supporting the sheet feeding operation of the regist roller 11 and intermediate feeding roller 12.

In the above case, the length DS of the portion that has not been passed through between the sheet supply roller 42 a and separating roller 42 b and still held by the rollers as shown in FIG. 4 is about 15 mm in the case of an A3 size printing sheet and about 27 mm in the case of an LD size printing sheet. The requisite minimum time (corresponding to the above predetermined time) for the portion that has not been passed through between the sheet supply roller 42 a and separating roller 42 b to be released from between them is as follows. A3 size sheet: 15 mm/420(mm/sec)=35.7 msec From this expression and taking into account a delay in clutch connection, the minimum requisite time of about 55 mmsec is obtained. LD size sheet: 27 mm/420(mm/sec)=64.2 msec From this expression and taking into account a delay in clutch connection, the minimum requisite time of about 85 mmsec is obtained.

Therefore, the duration of the support control needs to be determined in accordance with the position of the sheet supply cassette from which the printing sheet is supplied and the size of the printing sheet. The determined contents should be stored in the MEMORY 105 for the support control to be performed by the controller.

As described above, during time t10 to t11, the first and second feeding rollers 51 and 52 use sheet supply speed to perform the support control for the sheet feeding operation of the regist roller 11 and intermediate feeding roller 12 which is performed at process speed. This eliminates the load applied on the regist roller 11 and intermediate feeding roller 12 when it is being held between the sheet supply roller 42 a and separating roller 42 b, thereby preventing motor step-out. From this, it is possible to reduce the size of a pulse motor that drives the intermediate feeding roller 12, resulting in reduction of the cost of the image forming apparatus 100. The regist roller 11 and intermediate feeding roller 12 feed the printing sheet at process speed until time t14 has come after the rear end of the printing sheet has completely passed through between the sheet supply roller 42 a and separating roller 42 b. At time t14, a printing process for the printing sheet is completed.

At time t15, a next printing sheet is fed from the sheet supply cassette 62. The support control for this printing sheet is performed during time t20 to time t21. After that, sheet resupply from the ADU 70 is performed during time t23 to time t29, and aligning control is performed during time t28 to time t29. In this example, the support control is not performed for the sheet resupplied from the ADU 70, but only process speed is used to feed the resupplied sheet for printing process during time t31 to time t35. During time t36 to time t39, a third sheet is fed from the sheet supply cassette 62 at sheet supply speed and is subjected to the support control during time t40 to time t41. In this example, time t10, time t20, and time t40 correspond to the predetermined timing at which the regist roller 11 starts feeding a skew corrected sheet.

As described above, in the image forming apparatus 100, the intermediate feeding roller 12, which is driven by a pulse motor, is disposed between a sheet discharge port at which the sheet discharges of the sheet feeding path 50 from the sheet supply cassette and ADU 70 meet and the regist roller 11, thereby realizing three-speed control, with the result that a sheet in the apparatus can be fed at sheet supply speed, process speed, and ADU speed. It can be seen from a comparison between FIGS. 5 and 7 that what is markedly different from the conventional image forming apparatus is that the support control is performed in an initial short time period during which a printing sheet that has been supplied from the sheet supply cassette is fed at process speed for a transfer process.

In the above image forming apparatus 100, the load of the sheet supply roller and separating roller generated when a large-size printing paper is supplied from the sheet supply cassette can be eliminated by a short-time drive of the feeding rollers, which eliminates the need to increase the size of a pulse motor that drives the intermediate feeding roller 12. For the same reason, ordinary motors can be used as motors other than the pulse motor that drives the intermediate feeding roller 12. Therefore, it is possible to economically manufacture the image forming apparatus at low cost.

In the above embodiment, a function that embodies the invention is previously recorded in the apparatus. Alternatively, however, it is possible to obtain the same function by downloading it from a network or by installing it from a recording medium that stores it on the apparatus. As the recording medium, any type of recording medium, such as a CD-ROM, can be used as far as it can store a program and is computer-readable. Further, the function obtained by the previous installation or download may realize its function by cooperating with an OS (Operating System) and the like.

While the present invention has been described in detail according to the specific embodiment, it will be apparent to those skilled in the art that variations and modifications are possible without deviating from the broad principles and spirit of the present invention.

As has been described above in detail, even if the rear end of a printing sheet is held between the sheet supply roller and separating roller at the time when the regist roller starts feeding the printing sheet to apply a load on the sheet feeding operation, the feeding rollers eliminates the load to thereby improve the sheet feeding operation of the intermediate feeding roller. Therefore, a small pulse motor can be used as a drive source of the intermediate feeding roller, contributing to cost reduction. 

1. An image forming apparatus comprising: a drive controller that controls the drive of feeding rollers disposed on the upstream side in the feeding direction relative to an intermediate feeding roller that feeds a sheet to a regist roller that performs skew correction for the sheet; and a timing determination section that determines the timing at which the regist roller starts feeding the skew corrected sheet after the skew correction, wherein when the timing determination section determines that a predetermined timing for the regist roller to start feeding the skew corrected sheet has come, the drive controller drives the feeding rollers by a predetermined time from the predetermined timing.
 2. An image forming apparatus comprising: a drive controller that controls the drive of feeding rollers disposed on the upstream side in the feeding direction relative to an intermediate feeding roller that feeds a sheet to a regist roller that performs skew correction for the sheet; a sheet size determination section that determines the sheet size in the feeding direction of a sheet to be subjected to the skew correction performed by the regist roller; and a timing determination section that determines the timing at which the regist roller starts feeding the skew corrected sheet after the skew correction, wherein in the case where the sheet size determination section determines that a sheet to be subjected to the skew correction performed by the regist roller is larger than a predetermined size, when the timing determination section determines that a predetermined timing for the regist roller to start feeding the skew corrected sheet has come, the drive controller drives the feeding rollers by a predetermined time from the predetermined timing.
 3. The image forming apparatus according to claim 1, wherein the predetermined time is a time needed from a predetermined timing to the time for the rear end of a sheet to be released from between the separating rollers in the case where the rear end of the skew corrected sheet is, at the predetermined timing, held between the separation rollers that supply the sheet to the sheet feeding path.
 4. A sheet feeding method comprising: a drive control step that controls the drive of feeding rollers disposed on the upstream side in the feeding direction relative to an intermediate feeding roller that feeds a sheet to a regist roller that performs skew correction for the sheet; and a timing determination step that determines the timing at which the regist roller starts feeding the skew corrected sheet after the skew correction, wherein when the timing determination step determines that a predetermined timing for the regist roller to start feeding the skew corrected sheet has come, the drive control step drives the feeding rollers by a predetermined time from the predetermined timing.
 5. A sheet feeding method comprising: a drive control step that controls the drive of feeding rollers disposed on the upstream side in the feeding direction relative to an intermediate feeding roller that feeds a sheet to a regist roller that performs skew correction for the sheet; a sheet size determination step that determines the sheet size in the feeding direction of a sheet to be subjected to the skew correction performed by the regist roller; and a timing determination step that determines the timing at which the regist roller starts feeding the skew corrected sheet after the skew correction, wherein in the case where the sheet size determination step determines that a sheet to be subjected to the skew correction performed by the regist roller is larger than a predetermined size, when the timing determination step determines that a predetermined timing for the regist roller to start feeding the skew corrected sheet has come, the drive control step drives the feeding rollers by a predetermined time from the predetermined timing.
 6. The sheet feeding method according to claim 4, wherein the predetermined time is a time needed from a predetermined timing to the time for the rear end of a sheet to be released from between the separating rollers in the case where the rear end of the skew corrected sheet is, at the predetermined timing, held between the separation rollers that supply the sheet to the sheet feeding path. 